The extraction of contaminants and/or the recovery of trace elements from liquids can involve considerable time, energy, and expense. Extraction and recovery processes are commonly performed in water purification, mining, and waste treatments. Water purification is a multimillion dollar industry involving a variety of commercially available products and processes. Typically water purification techniques include: boiling, carbon filtering, distillation, reverse osmosis, ion exchange, and electrodeionization. While these techniques can be effective, they can also be cost-prohibitive.
Mining involves the process of extracting minerals from the earth. The mining industry uses a variety of physical and chemical extraction methods including grinding, crushing, washing, blasting, froth flotation, solvent extraction, smelting, electrostatic separation, magnetic separation, etc. While these techniques are well known, they can also be cost-prohibitive and inefficient.
Waste treatments generally involve the removal of specific contaminants from matter by techniques that change the physical, chemical, or biological character of the waste, to reduce its volume and/or toxicity, and to make the waste safer for disposal. Waste treatments are designed based on the physical and chemical properties of the waste. For example, for simple solid combustible materials, incineration can be used as a method of disposal. For mixed solid and liquid residential waste, compaction in landfills is typically used. While both methods have been employed for centuries, neither is optimal for the treatment of waste comprised substantially of liquids.
Compaction generally removes air from solid waste thereby reducing the overall volume. However, liquid waste contains only an insignificant amount of gas, and therefore, compaction offers little to no value. Incineration of solid waste requires little energy as the combustion reactions are generally self-sustaining. However, the combustion of most liquids is not self-sustaining and requires a continual source of energy to sustain the reaction thereby becoming cost prohibitive. Even if liquid waste could be changed readily from a liquid to a gas, such a transformation may not be desirable due to pollutants present in the waste, which may become airborne with the liquid. A more efficient means to handle liquid waste is generally to remove any contaminants from the liquid and to either reuse or return the liquid to the environment.
For example, typically, sewage treatment involves three stages, referred to as primary, secondary, and tertiary treatments. First, the solids are separated from the wastewater stream. Second, dissolved biological matter is progressively converted into a solid mass by using indigenous, water-borne bacteria. Finally, the biological solids are neutralized then disposed or re-used, and the treated water may be disinfected chemically using natural or synthetic resins or physically by lagooning or micro-filtration. The final effluent can be discharged into a natural surface water body (stream, river or bay) or other environment (wetland, golf course, greenway, etc.).
Commercial waste treatments generally involve more complex treatments due to the nature of the waste. For example, wastewater from metal mines and ore recovery plants are inevitably contaminated by the minerals present in the native rock formations. Typical contaminants include: iron, chromium, cobalt, uranium, mercury, nickel, antimony, arsenic, aluminum, cadmium, lead, manganese, copper, and zinc in various forms. Similarly, acceptable standards for certain contaminant ions in potable water continue to decrease. Various methods have been used to reduce these contaminants including chemical precipitation, ion exchange, reverse osmosis, solvent extraction (liquid ion exchange), electrodialysis, and chemical reduction. However, these procedures can have disadvantages such as limited metal or contaminant removal, high reagent and energy requirements, exorbitant costs, and generation of toxic sludge or other waste products requiring further disposal.
As such, advances in cost effective techniques and processes for isolation and removal or recovery of inorganic contaminants and trace elements from liquids, which are commercially feasible, continue to be sought through ongoing research and development efforts.